Method for restoring photosensitivity in hydrogen or deuterium loaded large diameter optical waveguide

ABSTRACT

The present invention provides a new and unique method for increasing the photosensitivity of a large diameter optical waveguide having a cross-section of at least about 0.3 millimeters. The method features loading the large diameter optical waveguide with a photosensitizing gas at a pressure at least about 4000 pounds per square inch (PSI) at a temperature of at least about 250° Celsius. The photosensitizing gas may be hydrogen, Deuterium or other suitable gas. The method also includes the step of using a particular large diameter optical waveguide having a core more than 1000 microns from the surface thereof. The method may be used as part of a process for writing a Bragg grating in an inner core or a cladding of the large diameter optical waveguide.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 10/459,653, filed on Jun. 10, 2003, which claimed the benefitof U.S. Provisional Patent Application Ser. No. 60/387,798, filed Jun.10, 2002 (CC-0325), which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention generally relates to a method for writing agrating in a large diameter optical waveguide; and more particularly toa method for writing a grating in a large diameter optical waveguide inwhich photosensitivity is restored or increased in a hydrogen orDeuterium loaded large diameter optical waveguide.

2. Description of Related Art

It is known in the art that the presence of hydrogen, Deuterium or othersuitable photosensitizing gases in a germanium doped waveguide enhancesthe photosensitivity of that waveguide. This is well documented innumerous references such as, “Photosensitive changes in Ge-doped fibersobserved by Raman spectroscopy,” D. McStay, SPIE vol. 1315 Fiber Optics'90, pp. 223-233; “Permanent photoinduced birefringence in a Ge-dopedfiber,” Francois Ouelette, Daniel Gagon, Michel Poirer, Applied PhysicsLetters, vol. 58, pp. 1813-1815, 1991; U.S. Pat. No. 5,235,659 “Methodof making an article comprising an optical waveguide,” Robert M. Atkins,Paul J. Lemaire, Victor Mizrahi, Kenneth L. Walker; Aug. 10, 1993; U.S.Pat. No. 5,287,427 “Method of making an article comprising an opticalcomponent, and article comprising the component,” Robert M. Atkins, PaulJ. Lemaire, Victor Mizrahi, Kenneth L. Walker; Feb. 15, 1994.

These prior art descriptions focus primarily on methods for increasingthe photosensitivity of fiber. Fiber has several unique characteristics.Optical fiber is typically coated with an organic polymer that cannotwithstand high temperatures. Single mode optical fiber is also typically80 or 125 microns in diameter. These characteristics drive the method bywhich the above references incorporate hydrogen into the optical fiber.In particular, very high temperatures are not employed, as this woulddamage the optical fiber coating. However, low temperatures limit thediffusion rate at which hydrogen is incorporated into the glass. For 125micron optical fiber, this not a terrible problem as at temperaturesbetween 50° C. and 80° C. (well below the damage temperatures for mostfiber coatings) significant hydrogen can be diffused into the fiber in areasonable time frame (less than 1 day). However, for significantlylarger glass structures the time frame quickly increases to excessivetimes.

Photosensitivity requirements can only be analyzed qualitatively atpresent. It was recognized from early in the development that therequirements were not met in the initial H2 loading iteration. Thecombination of a low photosensitivity waveguide and a concentration of−1.44×10ˆ20 ions/cmˆ3 of H2 were not sufficient to allow gratings to becollocated without undesirable out-of-band spectral characteristics. Toadd a third collocated grating, it was necessary to increase thepressure by a factor of 6 and the temperature was reduced 25° C. Theresulting H2 concentration increased to −5.47×10ˆ20 ions/cmˆ3, as shownin FIG. 1. This higher concentration has now been certified assufficient. However, the time required to reach 95% saturation, 21 days,is excessive and must be reduced to achieve a reasonable cycle time. Thenext step will be to determine the effects of raising and must bereduced to achieve a reasonable cycle time. The next step will be todetermine the effects of raising the temperature by 15-20% (absolute),to 250-275° C., which would reduce the loading time to 3-4 days and theconcentration to 3.46×10ˆ20 ions/cmˆ3, as shown. Provided that there isstill sufficient photosensitivity after the solubility losses, anadditional step would be to determine if the pressure could also bereduced without causing the sideband issue to reoccur when collocatinggratings.

The plot in FIG. 1 was constructed using the hydrogen diffusionequations for glass and illustrates the time issues more clearly. Forcylindrical geometries of 2000 microns, the time to reach a reasonablediffusion equilibrium is many days, perhaps even weeks at lowtemperatures.

SUMMARY OF THE INVENTION

In its broadest sense, the present invention provides a new and uniquemethod for increasing the photosensitivity of a large diameter opticalwaveguide having a cross-section of at least about 0.3 millimeters (alsoknown herein as “cane”). The method features loading the large diameteroptical waveguide with a photosensitizing gas at a pressure set toprovide a predetermined level of saturation based on a desired timerequirement and at a temperature of at least about 250 degrees Celsius.In a preferred embodiment, the pressure is set at at least about 4000pounds per square inch (PSI).

The photosensitizing gas may be hydrogen, Deuterium or other suitablegas. The scope of the invention is not intended to be limited to anyparticular photosensitizing gas or actinic radiation (typicallyultraviolet (UV) light) used to write the grating.

The method also includes the step of using a particular large diameteroptical waveguide having a core more than 1000 microns from the surfacethereof.

The method may be used as part of a process for writing a Bragg gratingin an inner core or a cladding of the large diameter optical waveguide.

The method also includes writing co-located Bragg gratings having thesteps of: waiting a predetermined period of time after writing a firstBragg grating for a substantial portion of the photosensitivity to berestored in the area in and around the selected part of the largediameter optical waveguide; and writing a second co-located Bragggrating in another part of the large diameter optical waveguide which issubstantially near the selected part of the large diameter opticalwaveguide having the first Bragg grating. This method has the addedadvantage of not requiring the additional step of re-loading thehydrogen or deuterium for restoring the photosensitivity. This allowsthe co-location of multiple gratings without the disadvantage of astrong anneal of the first grating relative to the subsequentgrating(s).

The present invention also provides a new and unique large diameteroptical waveguide having a cross-section of at least about 0.3millimeters made by performing the steps recited in either of theaforementioned methods, or both in combination.

The foregoing and other objects, features and advantages of the presentinvention will become more apparent in light of the following detaileddescription of exemplary embodiments thereof.

BRIEF DESCRIPTION OF THE DRAWING

The drawing, not drawn to scale, include the following Figures:

FIG. 1 is a graph of temperature (in Celsius degrees) versus time (indays) showing various times to reach a 95% of equilibrium value for fouroptical waveguides having different outer diameters.

FIG. 2 is a graph of temperature (in Celsius degrees) versusconcentration (in ions per cubic centimeter) showing equilibriumconcentration of hydrogen in Silica for seven different concentrations.

FIG. 3 is a diagram of a large diameter optical waveguide havingco-located Bragg gratings written therein.

BEST MODE FOR CARRYING OUT THE INVENTION Method for Increasing thePhotosensitivity in Hydrogen or Deuterium Loaded Large Diameter OpticalWaveguides

Given the previously documented advantages of the cane material's use intuning and athermalizing fiber Bragg gratings, it is desirable to beable to increase the photosensitivity of the cane to enable a widerrange of products to be constructed than can be constructed using thecane's inherent photosensitivity. However, the excessively longdiffusion times render the standard hydrogen loading methods unsuitablefor a large-scale production environment. Fortuitously, cane does notrequire an organic overcoat in order to maintain long-term reliability.To this end, much higher temperatures can be employed to shorten thetime needed to diffuse the hydrogen into the fiber. In particular, canegreater than 2000 microns in diameter is used. A quick examination ofthe chart above shows that for load times significantly less than 1 week(still long for manufacturing process), Temperatures greater than 250°C. are desirable. Initially, a straightforward extension of the previousart was attempted as a means of increasing the photosensitivity of thecane to the level in which gratings of appropriate quality could bemade. However, this straightforward increase in temperature failed toproduce the desired increase in photosensitivity. Extensive furtherstudy showed that the solubility of hydrogen in glass declines withincreasing temperature. To this end, equilibrium was achieved faster athigher temperatures, but the photosensitivity at constant pressure, wasnot sufficient to achieve desired goals. The figures below shows thetheoretical equilibrium concentration of hydrogen at the cane core forvarious pressures and temperatures.

In FIG. 2, it is clear that at temperatures greater 250° C., pressuresgreater than 4000 psi are required in order to get close to the desiredgoal. These pressures and temperatures are not easily achieves safely ina production environment and considerable effort was put into designingan building a system that could do so. To this end, the presentinvention provides a method for increasing the photosensitivity of caneto levels needed to write state of the art Bragg gratings by usingpressures set to provide a predetermined level of saturation based on adesired time requirement (preferably in excess of at least about 4000psi) and temperatures in excess of at least about 250° C. There is noknown method in the prior art that discloses this combination ofpressures and temperatures for hydrogen induced photosensitization ofthe glass. However, this method is quite useful for cane based devicesand may also be useful for photowritten gratings in glass basedintegrated optical devices in which the core is more than 1000 micronsfrom the glass surface.

Method for Restoring Photosensitivity in Hydrogen or Deuterium LoadedLarge Diameter Optical Waveguides

In general, the other feature of a collocated grating writing process isthe “hold” period that is utilized between writing gratings. The levelphotosensitivity required to write one 5 millimeter grating to thespecifications required for an optical device such as a tunable bandpassfilter is not large compared to some other 50 GHz gratings currentlywritten. However, that required for writing three collocated gratingsthat all conform to desired specifications is quite large. The “hold” isthe method that has been developed to allow the process to occur withoutthe need to H2 load multiple times. This technique is a byproduct ofusing a large diameter waveguide. By H2 loading the core of thewaveguide to a saturation condition, the surrounding cladding becomes areservoir of available H2. When a grating is written, the region wherethe index change occurs becomes depleted of hydrogen. The relativelyhigh partial pressure of the surrounding H2 forces diffusion to occur inthe direction of the depleted core. The time required for the diffusionto substantially occur is on the order of 14-24 hours at 25□ C.corresponding to a depletion radius on axis of about 30 microns. Thiscalculation was verified by experiments where the center wavelengths ofgratings were measured in-situ at various temperatures after to monitorthe change in H2 concentration. Of note is that the re-established H2concentration then allowed a grating to be written which was notpossible immediately after the first. This establishes the fact that notjust the H2 concentration was re-established, but also thephotosensitivity.

In particular, the present invention provides a method for writingco-located Bragg gratings 22 a, 22 b in a large diameter opticalwaveguide 40 having a cross-section of at least about 0.3 millimetersshown in FIG. 3. The method features the steps of:

writing a first Bragg grating 22 a in a selected part generallyindicated as 40 a of the large diameter optical waveguide 40;

waiting a predetermined period of time after writing the first Bragggrating 22 a for a substantial portion of the photosensitivity to berestored in the area in and around the selected part 40 a of the largediameter optical waveguide; and

writing a second co-located Bragg grating 22 b in another part generallyindicated as 40 b of the large diameter optical waveguide 40 which issubstantially near the selected part 40 a of the large diameter opticalwaveguide 40 having the first Bragg grating 22 a.

The method may be used together with the method discussed above to alsoinclude the step of loading the large diameter optical waveguide 40 witha photosensitizing gas at a pressure at least about 4000 pounds persquare inch (PSI) at a temperature of at least about 250 degreesCelsius.

In effect, this method involves waiting a predetermined period of time,after writing the Bragg Grating 22 a in the waveguide for a substantialportion of the photosensitivity to be restored. This effect is producedby having a large quantity of molecular hydrogen or deuterium stored insolution in the glass waveguide. The time required to achieve maximumphotosensitivity is determined by three factors: initial concentrationof dissolved hydrogen or deuterium; temperature; and the distance fromthe depleted or reduced photosensitive area of the waveguide to theun-depleted store of dissolved hydrogen.

As shown in FIG. 3, the large diameter optical waveguide 40 has an innercore 42 and an outer cladding 44 surrounding the inner core 42, opposingends 41 a, 41 b, and a diameter D of at least about 0.3 millimeters,similar to that disclosed in the aforementioned co-pending U.S. patentapplication Ser. No. 09/455,868 (CC-0230), which is hereby incorporatedby reference. The inner core 42 has the Bragg grating 22 a writtentherein for tuning by applying a compressive force indicated by arrows48 on the opposite ends 41 a, 41 b of the optical waveguide 40, or forsensing an external parameter like pressure applied thereon.

Cane waveguides have proven to be useful elements for creating highlyreliable tunable grating based elements, and appear to be suitable for avariety of other applications.

One of the issues associated with the tuning of cane waveguides is theforce required to tune a given cane element (typically formed in a“dogbone” element). Reducing the cane diameter can reduce the forcerequired to tune a grating a given amount; however, the element willbuckle at a lower compression strain, ultimately producing a lowertuning range.

The large diameter optical waveguide 40 comprises silica glass (SiO₂)based material having the appropriate dopants, as is known, to allowlight indicated by arrow 45 to propagate in either direction along theinner core 42 and/or within the large diameter optical waveguide 40. Theinner core 42 has an outer dimension d_(c) and the large diameteroptical waveguide 40 has an outer dimension D. Other materials for thelarge diameter optical waveguide 40 may be used if desired. For example,the large diameter optical waveguide 40 may be made of any glass, e.g.,silica, phosphate glass, or other glasses; or solely plastic.

The outer dimension D of the outer cladding 44 is at least about 0.3millimeters; and the outer dimension d_(c) of the inner core 42 is suchthat it propagates only a few spatial modes (e.g., less than about 6).For example for single spatial mode propagation, the inner core 42 has asubstantially circular transverse cross-sectional shape with a diameterd_(c) less than about 12.5 microns, depending on the wavelength oflight. The invention will also work with larger or non-circular coresthat propagate a few (less than about 6) spatial modes, in one or moretransverse directions. The outer diameter D of the outer cladding 44 andthe length L have values that will resist buckling when the largediameter optical waveguide 40 is placed in axial compression asindicated by the arrows 48.

The large diameter optical waveguide 40 may be ground or etched toprovide tapered (or beveled or angled) outer corners or edges 50 toprovide a seat for the large diameter optical waveguide 40 to mate withanother part (not shown herein) and/or to adjust the force angles on thelarge diameter optical waveguide 40, or for other reasons. The angle ofthe beveled corners 50 is set to achieve the desired function. Further,the large diameter optical waveguide 40 may be etched or ground toprovide nubs 52 for an attachment of a pigtail assembly 54 (not shownherein) to the large diameter optical waveguide 40. Further, the size ofthe large diameter optical waveguide 40 has inherent mechanical rigiditythat improves packaging options and reduces bend losses.

In the large diameter optical waveguide 40, the Bragg grating 22 a isimpressed (or embedded or imprinted) therein. A Bragg grating 22 a, asis known, is a periodic or aperiodic variation in the effectiverefractive index and/or effective optical absorption coefficient of anoptical waveguide, such as that described in U.S. Pat. Nos. 4,725,110and 4,807,950, entitled “Method for Impressing Gratings Within FiberOptics”, to Glenn et al.; and U.S. Pat. No. 5,388,173, entitled “Methodand Apparatus for Forming Aperiodic Gratings in Optical Fibers”, toGlenn, which are hereby incorporated by reference to the extentnecessary to understand the present invention. The aperiodic variationof the gratings described herein may include a chirped grating. See alsoU.S. Pat. Nos. 5,042,897 and 5,061,032, both issued to Meltz et al., andhereby incorporated by reference in their entirety. As shown, thegrating 22 a is written in the inner core 42; however, the scope of theinvention is intended to include writing the grating in the outercladding 44, as well as a combination of the inner core 42 and the outercladding 44. Any type of wavelength-tunable grating or reflectiveelement embedded, etched, imprinted, or otherwise formed in the largediameter optical waveguide 40 may be used. The large diameter opticalwaveguide 40 may be photosensitive if the grating 22 a is to be writteninto the large diameter optical waveguide 40. As used herein, the term“grating” means any of such reflective elements. Further, the reflectiveelement (or grating) 22 a may be used in reflection and/or transmissionof light. The incoming light 57 incident on the grating 22 a reflects aportion thereof as indicated by a line 58, and passes the remainingincident light 57 (within a predetermined wavelength range), asindicated by a line 60 (as is known).

The grating 22 a has a grating length Lg, which is determined based onthe application, and may be any desired length. A typical grating 22 ahas a grating length Lg in the range of about 3-40 millimeters. Othersizes or ranges may be used if desired. The length Lg of the grating 22a may be shorter than or substantially the same length as the length Lof the large diameter optical waveguide 40. Also, the inner core 42 neednot be located in the center of the large diameter optical waveguide 40but may be located anywhere in the large diameter optical waveguide 40.

Accordingly, an outer diameter D of greater than about 400 microns (0.4millimeters) provides acceptable results (without buckling) for awaveguide length L of 5 millimeters, over a grating wavelength tuningrange of about 10 nm. For a given outer diameter D as the length Lincreases, the wavelength tuning range (without buckling) decreases.Other diameters D for the large diameter optical waveguide 40 may beused depending on the overall length L of the large diameter opticalwaveguide 40 and the desired amount of compression length change ΔL orwavelength shift Δλ.

The large diameter optical waveguide 40 may be made using fiber drawingtechniques that provide the resultant desired dimensions for the coreand the outer diameter discussed hereinbefore. As such, the externalsurface of the large diameter optical waveguide 40 will likely beoptically flat, thereby allowing Bragg gratings to be written throughthe cladding similar to that which is done for conventional opticalfiber. Because the large diameter optical waveguide 40 has a large outerdiameter compared to that of a standard optical fiber (e.g., 125microns), the large diameter optical waveguide 40 may not need to becoated with a buffer and then stripped to write the gratings, therebyrequiring less steps than that needed for conventional optical fibergratings. Also, the large outer diameter D of the large diameter opticalwaveguide 40, allows the waveguide to be ground, etched or machinedwhile retaining the mechanical strength of the large diameter opticalwaveguide 40. The large diameter optical waveguide 40 is easilymanufacturable and easy to handle, and may be made in long lengths (onthe order of many inches, feet, or meters) then cut to size as neededfor the desired application.

Also; the large diameter optical waveguide 40 does not exhibitmechanical degradation from surface ablation common with optical fibersunder high laser fluency (or power or intensity) during grating exposure(or writing). In particular, the thickness of the cladding between thecladding outer diameter and the core outer diameter causes a reducedpower level at the air-to-glass interface for a focused writing beam.

The large diameter optical waveguide 40 also reduces coupling betweenthe core and cladding modes due to the increased end cross-sectionalarea between the core and cladding of the waveguide. Thus, the gratings22 a written in the inner core 42 of the large diameter opticalwaveguide 40 exhibit less optical transmission loss and exhibits acleaner optical profile than a conventional fiber grating because thelarge cladding region dissipates coupled cladding modes, therebyreducing the coupling of the inner core 42 to the outer cladding 44modes. In general, the greater the difference in the cross-sectionalarea between the inner core 42 and the outer cladding 44 the smaller themode field overlap and the lower the coupling to the cladding modes. Thethickness of the outer cladding 44 between the cladding outer diameterand the core outer diameter may be set to optimize this effect. Otherdiameters of the inner core 42 and the large diameter optical waveguide40 may be used if desired such that the cladding modes are reduced tothe desired levels.

The large diameter optical waveguide 40 may have end cross-sectionalshapes other than circular, such as square, rectangular, elliptical,clam-shell, octagonal, multi-sided, or any other desired shapes,discussed more hereinafter. Also, the waveguide may resemble a short“block” type or a longer “cane” type geometry, depending on the lengthof the waveguide and outer dimension of the waveguide.

Finally, a similar effect for restoring photosensitivity is alsopossible in optical fiber but may (or may not) require repeating theinitial procedure used for hydrogen or deuterium loading. The maindifference between the claims is the amount of additionalphotosensitivity available without the possible additional re-loadingstep. This step is not required for large diameter waveguides due to thelarge supply to stored hydrogen available.

The Scope of the Invention

It should be understood that, unless stated otherwise herein, any of thefeatures, characteristics, alternatives or modifications describedregarding a particular embodiment herein may also be applied, used, orincorporated with any other embodiment described herein.

For example, although the invention is described in relation to longperiod gratings, the inventors envision other embodiments using blazedgratings, periodic or aperiodic gratings, or chirped gratings.

Although the invention has been described and illustrated with respectto exemplary embodiments thereof, the foregoing and various otheradditions and omissions may be made therein without departing from thespirit and scope of the present invention.

1. A method for writing co-located gratings in a large diameter opticalwaveguide, the method comprising: writing a first grating in a selectedpart of the large diameter optical waveguide having an outer transversedimension of at least about 0.3 millimeters; waiting a period of timeafter writing the first grating for a portion of the photosensitivity tobe restored in the area at the selected part of the large diameteroptical waveguide; and writing a second grating in the large diameteroptical waveguide such that at least a portion of the first grating andsecond grating are co-located.
 2. The method according to claim 1,further includes the step of loading the large diameter opticalwaveguide with a photosensitizing gas.
 3. The method according to claim2, wherein the photosensitizing gas is hydrogen.
 4. The method accordingto claim 2, wherein the photosensitizing gas is deuterium.
 5. The methodaccording to claim 1, further includes loading the large diameteroptical waveguide with a photosensitizing gas at a pressure at leastabout 4000 pounds per square inch (PSI) at a temperature of at leastabout 250 degrees Celsius; and writing at least one Bragg grating in aselected part of the large diameter optical waveguide.
 6. The methodaccording to claim 1, wherein the waiting a period of time includeswaiting a period of time to permit a sufficient amount ofphotosensitizing material to rediffuse into the selected portion of thelarge diameter optical waveguide.
 7. The method according to claim 1,wherein the large diameter waveguide has an inner core disposed within aouter cladding.
 8. The method according to claim 7, wherein the theinner core greater than 1000 microns from the outer surface thereof. 9.The method according to claim 7, wherein the writing of the first and/orsecond grating includes writing at least the first and/or second gratingin the inner core of the large diameter optical waveguide.
 10. Themethod according to claim 7, wherein the writing of the first and/orsecond grating includes writing at least the first and/or second gratingin the outer cladding of the large diameter optical waveguide.
 11. Themethod according to claim 1, wherein the first and second gratings areBragg gratings.
 12. The method according to claim 1, wherein the firstand second gratings are substantially co-located.
 13. The methodaccording to claim 1, wherein waiting a period of time is substantial topermit the photosensitivity to be substantially restored to the selectedpart of the large diameter waveguide.
 14. The method according to claim1, wherein the writing of the first and second grating includes exposingthe large diameter optical waveguide to ultraviolet light.
 15. Themethod according to claim 1, wherein the large diameter opticalwaveguide has an outer transverse dimension greater than 0.9millimeters.
 16. The method according to claim 1, wherein the outertransverse dimension of the large diameter optical waveguide is at least0.3 millimeters, 0.4 millimeters, 0.5 millimeters, 0.6 millimeters, 0.7millimeters, 0.8 millimeters, 0.9 millimeters, 1.0 millimeters, 1.1millimeters, 1.2 millimeters, 1.3 millimeters, or 1.4 millimeters orgreater.
 17. The method according to claim 1, wherein said outertransverse dimension of the large diameter optical waveguide is greaterthan about the dimension selected from the group consisting of 0.5 mm,0.6 mm, 0.7 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.4 mm, 1.6 mm, 1.8 mm, 2.0 mm,2.1 mm, 2.3 mm, 2.5, mm, 2.7 mm, 2.9 mm, 3.0 mm, 3.3 mm, 3.6 mm, 3.9 mm,4.0 mm, 4.2 mm, 4.5 mm, 4.7 mm, 5.0 mm, 6.0 mm, 7.0 mm, 8.0 mm, 9.0 mm,1.0 cm, 5.0 cm, 10.0 cm, and 20.0 cm.
 18. The method according to claim1, wherein the large diameter waveguide having a length along alongitudinal direction greater than about the dimension selected fromthe group consisting of 3 mm, 5 mm, 7 mm, 9 mm, 10 mm, 12 mm, 14 mm, 16mm, 18 mm, 20 mm, 21 mm, 23 mm, 25, mm, 27 mm, 29 mm, 30 mm, 32 mm, 34mm, 36 mm, 38 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, 65 mm, 70 mm, 75mm, 80 mm, 85 mm, 90 mm, 95 mm, 100 mm, 20 cm, 30 cm, 40 cm, 50 cm and100 cm.
 19. A large diameter optical waveguide made by performing thesteps recited in claim 1.